The court heard how the passing arm first collided with Ms Dew’s car before striking her, pinning her against the second car.

Christine Dew

Giving evidence at day two of the trial was Mark Richards, a police forensic collision investigator.

He explained how officers closed the A390 for a test run using the same tractor driven by Bird. The court was shown footage, from a following police car, of how the left arm of the slurry spreader fell slowly out of position as it turned a corner.

Mr Richards said the arms were held upright and only slightly inclined inwards.

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He said they could easily fall out of position through gravity if the hydraulic pressure was released.

However he said two police officers failed to pull down the arm in a test if the hydraulic system was ‘locked’ by controls inside the tractor.

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He said: “The principle effect of that switch is that it disables the touch any of the other controls – to stop the driver of the tractor touching any of the buttons.

“A consequence of that is that it seals effectively the tractor spool value controls. It closes them down so there is no transfer of oil to whatever hydraulic equipment is attached.

“That lock switch does not lock the arms attached to the spreader at all does it?”

Mr Richards replied: “No, it only affects the tractor.”

The A390 at St Mewan near St Austell and the grass verge on the left where two cars had stopped after a minor collision (Image: Goggle)

Mr Wiseman continued: “That slurry spreader has no mechanical, secondary device – no chain or padlock – nothing to firmly hold these arms in position. It does not have any hydraulic check to retain pressure.

“In fact, this manufacturing design is condemned by the Health and Safety Executive. It is wholly defective. Is that right?”

“Yes,” replied Mr Richards.

Mr Wiseman added: “And the supply of this equipment is unlawful. It is stated that it is dangerous. Would you agree it is dangerous?”

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Mr Richards replied: “I would agree there should have been something (a secondary safety device) fitted.”

Following questions from Mr Wiseman, Mr Richards confirmed that there was no warning sound or light to alert the driver that an arm was out of position. Neither did lowering the arms make a noise which could be heard by the driver.

The court heard both the tractor and slurry spreader were in serviceable condition with no mechanical defects.